Viscose from Recycled Cotton
Researchers at Lund University in Sweden have succeeded in making new viscose – from worn-out cotton sheets.
“Old textiles around the world end up at the rubbish tip and are often burned. In Sweden, they are generally burned to produce district heating. Extensive development work is being conducted to give old clothes and textiles a worthier end,” the Swedish university wrote. The planet would need recycled textiles, “as it takes a lot of energy, water and land to cultivate cotton and other plant sources for textiles”. But there are many challenges. “Cellulose chains, the main component in plant fibers, are complex and long. Cotton textiles are also intensively treated with dyes, protective agents and other chemicals. And then there is all the ingrained grime in the form of skin flakes and fats,” explained Edvin Bågenholm-Ruuth, doctoral student in chemical engineering at Lund University.
As reported by Lund University, he and his colleagues have now found a way to loosen up and convert the complex cotton fibers into viscose fibers. Viscose – sometimes referred to as artificial silk – is a common constituent of clothes such as blouses, skirts and dresses. The raw material is cellulose, in most cases wood.
A new technique, developed by Edvin Bågenholm-Ruuth and his colleagues, could soon be a commercial proposition that instead produces viscose from recycled textiles – and therefore saves on valuable forest resources, the university informed. “There are already viscose variants that are to some extent produced using old cotton fibers. However, a satisfactory product often requires a high percentage of ‘virgin’ fiber. Late last year, the researchers published a study that shows the process (https://link.springer.com/article/10.1007/s10570-023-05646-2). In the coming years, there are plans for a pilot plant somewhere in Europe. The method has already been tested regarding the spinning of viscose threads, and the results were excellent.”
From the current perspective, it looks like the process will not be expensive. “It requires a quite simple salt – zinc chloride – which dissolves in water. Another advantage is that a smaller percentage of the toxic substance carbon disulfide is needed compared to standard processes. The result is good-quality viscose fiber, even though the process needs to be further optimized. “We have used white textiles, but if you use old, dyed clothes, you may need to add a stage that decolorizes the clothes. If this can be done while also avoiding traditional bleaching, it is preferable, as bleaching is a very resource-intensive process with a considerable environmental impact,” Edvin Bågenholm-Ruuth was cited.
The process
According to the information, the textiles are placed in a zinc chloride solution, and within one hour, everything is transformed into a gooey mass. Then water is added, leading to the precipitation of a fluffy white mass known as a “dissolving pulp”, which can be filtered off from the liquid. This pulp can then replace the wood pulp used in today’s viscose process. In the next stage, the pulp is treated with several chemicals, including carbon disulfide, to make it soluble in sodium hydroxide. The pulp is dissolved, spun, and then cut into viscose fibers.
Production
A company, ShareTex, has been formed to apply the technology and the hope is that this could happen on a commercial scale within five to seven years.
(Published in GLOBAL RECYCLING Magazine 2/2024, Page 35, Photo: Iren / pixabay.com)
